This invention relates generally to method and apparatus applicable to a cooking appliance incorporating an automatic surface unit, and more particularly to method and apparatus for detecting a surface unit temperature sensor failure in such an appliance and modifying the mode of operation of the automatic surface unit accordingly.
An automatic surface unit is equipped with a temperature sensor for sensing the temperature of the utensil being heated by the surface unit and a controller for controlling the energization of the surface unit as a function of the sensed utensil temperature. Such surface units are well known in the art. Typically, such surface units include a temperature sensing device such as a bi-metallic device or a thermistor device mounted to be in thermal contact with the utensil. When the sensed temperature is less than a predetermined threshold temperature set by a user manipulation of input control knobs or switches mechanically coupled to the sensor device, the heating element is energized at full power. When the temperature exceeds the threshold the heating element is de-energized. An electronic control system for an automatic surface unit in which the electromechanical sensing and control devices are replaced by a microprocessor based control arrangement is described in commonly assigned U.S. Pat. No. 4,493,980, which is hereby incorporated by reference.
A problem common to both the electromechanical and the electronic temperature sensing arrangements for automatic surface units is that a failure in the sensor circuitry typically results in either the surface unit being operated at full power continuously or the surface unit being totally de-energized. The user, being unaware of the failure, may be greatly inconvenienced by either overheating or underheating a dish. Furthermore, even if aware of the failure, the user is unable to make productive use of that surface unit until the sensor is repaired or replaced.
It would be desirable to provide an arrangement for automatically detecting the occurrence of a failure of the sensor, informing the user of the existence of the failure, and enabling the user to continue to use the surface unit as a non-automatic surface unit during the interim until the surface unit is repaired at the user's convenience.
It is therefore an object of the present invention to provide an improved control arrangement for a cooking appliance featuring an automatic surface unit which automatically detects the failure of the temperature sensor and provides a signal to the user indicative of the occurrence of such a failure.
It is a further object of the invention to provide a control arrangement of the aforementioned type which enables the user to continue to use the surface unit after the occurrence of a sensor failure as a non-automatic or regular surface unit.